外场对分子纳米结电流-电压特性的影响

针对由金属电极/分子/金属电极组成的分子纳米结,应用扩展主方程的方法,考虑分子纳米结中影响其传输过程的外场、分子内的弛豫过程等因素研究了在外场作用下分子纳米结内的稳定电流和瞬间电流.由于分子内较强的电子-振动耦合,分子纳米结中的电流-电压曲线呈现台阶式非弹性特征.在不同的高斯型脉冲的激发作用下,分子纳米结中电流需要达到稳定的时间也不相同,脉冲宽度在1ps时瞬间电流现象明显,这时分子处于非平衡分布,分子两端的电流存在较大差异.随着脉冲宽度和外场偏压的增加,分子两端的电流趋于平衡.     

光激发下分子纳米结中电荷输运的振动效应研究

在纳米金属电极和分子组成的分子纳米结中,应用分子振动的简正坐标在弱耦合近似下研究了在光激发作用下电荷的输运过程,并从电离能的角度分析了顺序电荷转移的机理,研究了在光激发条件下分子纳米结的电流-电压特性. 发现分子的振动效应是Franck-Condon阻滞在光激发作用下消失的关键因素,进而在理论上分析了分子的电离能在电荷输运中的作用,同时分析了IVR效应对光激发下分子纳米结中电荷输运的影响. 关键词： Franck-Condon阻滞 振动效应 电流-电压特性     

金属电极与分子中非弹性电流的理论研究

考虑分子的振动能级,在简正反应坐标下研究了通过"金属/分子/金属"所组成系统的非弹性电流.研究发现非弹性电流传输过程中分子不同带电态的能量的相对位形对Franck-Condon阻滞有较强的影响,进而在理论上分析了分子的稳定态与Franck-Condon阻滞的关系,以及分子内部的振动能量分布、分子与金属电极的相对位置与系统的电流-电压曲线的关系.     

光激发作用下分子与多金属纳米粒子间的电荷转移研究

金属纳米粒子在光激发作用下的增强作用是纳米科学领域的一个研究热点. 针对分子和多个不同位形下的金属纳米粒子在光激发下的相互作用展开了理论研究. 应用密度矩阵理论描述分子和金属纳米粒子同时激发产生表面等离激元后的电荷输运过程. 研究发现, 表面等离激元增强效应与分子和各个金属纳米粒子的相对位置有密切关系. 详细分析了金属纳米粒子间的耦合强度、分子和金属纳米粒子间的耦合强度、表面等离激元能级杂化、分子激发能和外场频率对表面等离激元增强效应的影响.     

异质结线性吸收谱中的等离激元效应

将染料分子与半导体表面所组成的异质结与金属纳米粒子的耦合系统作为研究对象,考虑分子的振动态,在偶极-偶极近似下研究其线性吸收谱及相关的电荷转移动力学过程. 对金属纳米粒子作用下吸收谱变宽及相关的电子转移增强过程作了仔细的分析和讨论,理论分析了金属钠米粒子的表面等离激元对异质结中超快电子转移的影响. 关键词： 金属纳米粒子 等离激元 异质结电荷转移     

金属电极对有机分子非弹性电子隧穿谱的影响

利用第一性原理计算金属电极下1,6-己二硫醇和1,4-二巯基苯分子结的非弹性电子隧穿谱,发现非弹性电子隧穿谱对金属电极的变化十分灵敏,并且非弹性电子隧穿谱的振动峰位置和强度与硫原子和金属电极表面的距离密切相关.结果表明电极材料和分子与金属成键的情况是影响分子结的非弹性电子输运的重要因素.理论分析进一步表明不同金属电极和有机分子的耦合能不同导致了谱峰强弱的调整.     

分子激发中的表面等离激元增强效应

金属纳米粒子的表面等离激元增强效应是纳米科学领域的一个研究热点.针对染料分子与金属纳米粒子的耦合系统,应用偶极-偶极近似计算分子与金属纳米粒子的库仑相互作用,并应用密度矩阵理论描述在不同极化方向的电场作用下的电荷输运过程,分析了分子与金属纳米粒子在不同相对位置下分子激发态的动力学过程,发现表面等离激元的增强效应与分子和金属钠米粒子的相对位置以及等离激元的耗散系数有密切关系,详细讨论了分子与金属纳米粒子间的耦合强度、外场的极化方向、等离激元的寿命及共振激发条件对分子激发态及表面等离激元增强的影响,分析了分子-金属纳米粒子耦合系统中表面等离激元增强效应的物理本质.     

高压耦合高功率脉冲磁控溅射的增强放电效应

等离子体源离子注入与沉积技术作为一种可生产高结合力、高致密度涂层的真空镀膜技术,具有广阔的应用前景,尤其适用于高载荷工况下服役的功能涂层制备.该技术中金属等离子体源是关键,而现有的脉冲阴极弧源结构复杂,且由于伴随"金属液滴"而需要增加过滤装置.本文研究了另一种简单结构的金属等离子体源备选一高功率脉冲磁控溅射源(HPPMS)的放电特性,采用等离子体发射光谱仪探索了不同的耦合高压对HPPMS放电靶电流特性和等离子体特性的作用.发现耦合高压对HPPMS放电有明显的促进作用,相同靶电压下的放电强度大幅增加,相对于金属放电,耦合高压对气体放电的促进作用更加明显,但在自溅射为主的高压放电阶段对金属放电的促进作用明显增强.讨论了耦合高压对HPPMS放电的增强机制,发现耦合高压自辉光放电、耦合高压和HPPMS电压构成双向负压形成的空心阴极效应,以及耦合高压鞘层改善的双极扩散效应都对HPPMS放电的增强有明显作用.     

ZnS修饰对ZnO纳米棒：P3HT复合薄膜I-V性质的影响

本文通过化学浴沉积法获得了直径约为50 nm, 长度约为250 nm的ZnO纳米棒阵列, 引入纳米ZnS对ZnO纳米棒进行表面修饰, 分别制备得到了具有ITO (indium tin oxides)/ZnO/Poly-(3-hexylthiophene) (P3HT)/Au和ITO/ZnO@ZnS/P3HT/Au结构的多层器件. 通过I-V曲线对比讨论了两种结构器件的开启电压, 串联电阻, 反向漏电流及整流比等参数, 认为包含ZnS修饰层器件的开启电压、串联电阻、反向漏电流明显降低, 整流比显著增强, 展现出更优异的电子传输性能. 光致发光光谱分析结果证实由于ZnS使ZnO纳米 棒的表面缺陷产生的非辐射复合被明显抑制, 弱化了电场激发下的载流子陷获, 改善了器件的导电特性. 关键词： ZnO纳米棒阵列 表面修饰 电流-电压特性     

超导-量子点耦合系统的相干输运

研究超导-量子点耦合系统的量子相干输运,主要考虑系统在微波场及Zeeman场作用下的输运电流特性.应用BCS平均场理论及非平衡格林函数技术,对超导体各极作Bogoliubov变换使其对角化,从而推导出用格林函数表示的电流公式.对几种特殊情况进行数值分析,计算出电流-电压、电流-磁场及直流Josephson电流的共振隧穿曲线.     

Adsorbate motions induced by vibrational mode coupling

Adsorbate motions are discussed with a primary attention focused on the coupling between a vibrational mode excited by ultrafast laser heated hot-electrons or by inelastic tunneling electrons with scanning tunneling microscope and the reaction coordinate (RC) mode. Recent experimental results have demonstrated an efficient reaction pathways involving an indirect excitation of a frustrated translational mode, rather than its direct excitation for adsorbate hopping on surfaces. Elementary processes are briefly described for hopping of CO molecules on a laser heated stepped Pt surface, where excitation of the frustrated rotation mode has been found to plays an indispensable. Calculation of the inelastic tunneling current (ITC) for excitation of the C-O stretch mode of a CO molecule is combined with a theory of anharmonic mode coupling to activate the frustrated translation mode above the barrier. The hopping rate as a function of the bias voltage agrees with the experimental result. An unified theory of single-, and two-electron processes for ITC-induced motions induced by an indirect excitation of the RC-mode via mode coupling is also applied to reproduce a crossover from hopping to desorption of a single NH₃ molecule on Cu(1 0 0) with an increase in the tunneling current.     

Theory of inelastic electric current through single molecules

An electronic structure theory has been developed for an inelastic electric current of electron-intramolecular vibration coupling origin in terms of the Keldysh Green function method and the self-consistent Born approximation. Numerical calculations were made for the benzenedithiol molecule linking the two Au(111) electrodes. The calculations successfully reproduce typical features commonly observed in inelastic tunneling spectroscopy. The vibrational excitation energy due to the inelastic current was estimated. The inelastic electric current is quite important for the structural stability and the switching possibility of the molecular device.     

红外激光场诱发下的多原子分子离解反应模型

本文在以前工作的基础上,继续讨论了多原子分子在红外激光场作用下产生多光子离解的机制,得到了分子各个振动模之间的非线性耦合方程组,以SF₆分子为例,数值计算了模-模间的能量转移时间、费密共振作用、各个模被激光场激发的程度,最后联系到单分子反应的模型,讨论了多原子分子的离解速率,基本上得到了与实验现象一致的结果。 关键词：     

An experimental test of symmetry selection rules in inelastic electron tunneling spectroscopy (IETS)

The inelastic electron tunneling spectrum of a highly symmetric molecule, anthracene, is presented. An analysis of the spectrum shows that the vibrational frequencies as measured by tunneling agree well with optical measurements. The high degree of symmetry of the molecule allows separation of the infrared, Raman, and optically inactive modes. The infrared and Raman active modes have comparable intensities; the optically inactive modes are much weaker. Analysis of these intensities within the framework of existing theories suggests that the coupling of tunneling electrons to the induced dipole moment of molecules is large and cannot be neglected.     

He和D_2分子相互作用转动激发研究

用T .T(K .T .TangandJ .Peter.Toennies)势模型和公认精密度较高的密耦 (Close Coupling)近似方法计算了E =0 .1eV和E =0 .2eV时 ,0 0— 0 0弹性碰撞及 0 0— 0 2、0 0— 0 4、0 0— 0 6非弹性碰撞 ,得出D2 分子转动激发分波截面 ,并得到了原子与分子碰撞弹性分波截面和非弹性激发截面随量子数增加的变化规律。     

Single molecule vibrationally mediated chemistry

Tunnelling electrons may scatter inelastically with an adsorbate, releasing part of their energy through the excitation of molecular vibrations. The resolution of inelastic processes with a low temperature scanning tunnelling microscope (STM) provides a valuable tool to chemically characterize single adsorbates and their adsorption mechanisms. Here, we present a molecular scale picture of single molecule vibrational chemistry, as resolved by STM. To understand the way a reaction proceed it is needed knowledge about both the excitation and damping of a molecular vibration. The excitation is mediated by the specific coupling between electronic molecular resonances present at the Fermi level and vibrational states of the adsorbate. Thus, the two-dimensional mapping of the inelastic signal with an STM provides the spatial distribution of the adsorbate electronic states (near the Fermi level) which are predominantly coupled to the particular vibrational mode observed. The damping of the vibration follows a competition between different mechanisms, mediated via the creation of electron-hole pairs or via anharmonic coupling between vibrational states. This latter case give rise to effective energy transfer mechanisms which eventually may focus vibrational energy in a specific reaction coordinate. In this single-molecule work-bench, STM provides alternative tools to understand reactivity in the limit of low excitation rate, which demonstrate the existence of state-specific excitation strategies which may lead to selectivity in the product of a reaction.     

Collective excitations in double quantum wells with strong tunnel coupling

Spectra of collective and magnetic excitations in symmetric double quantum wells with strong tunnel coupling were studied by inelastic scattering. Gaps in the spectrum of collective and single-particle excitations associated with tunnel interwell splitting were measured. New excitation modes, namely, tunnel Bernstein modes, were detected in a magnetic field. Based on the dispersion and magnetic-field dependences of the energies of inelastic light scattering lines, a classification of excitations and magnetic excitations was given.     

Satellite band in the rovibrational spectrum of CO2 in helium droplets

Pulsed infrared (nu approximately 2350 cm(-1)) laser excitation spectra of CO2 molecules embedded in helium droplets are reported. The spectra exhibit a sharp R(0) rovibrational line accompanied by a weak broader (deltanu approximately 10 cm(-1)) satellite band, which is shifted by 14 cm(-1) towards higher frequencies. We assign this satellite band to a simultaneous rovibrational excitation of a molecule and its helium solvation shell. The results are rationalized within a model, which includes coupling of the rotational states of a molecule and a ring of He atoms.